A pump of the afore-mentioned type is disclosed by DE-OS 29 12 935. The pump described therein is provided for use in an anti-locking hydraulic braking system. To minimize the noise emission of the pump during operation, it is provided to add to the pressure valve a damping chamber, a check valve and a restrictor.
The pressure valve and the check valve are formed within a valve carrier suitable to be inserted into the pump casing. A cup-shaped support is screwed into the casing to hold the valve carrier. Provided between a front side of the valve carrier and the bottom of the cup is an expansion chamber confined by a hard-elastic rubber element. The element is intended to accommodate pressure peaks in the pressure fluid at the outlet of the pump that would cause noises in the connected braking system.
It is the object of the invention to further reduce this noise.
DE-OS 28 51 134 discloses an anti-locking hydraulic braking system, wherein a lightly prestressed reservoir is provided on the output of the pump. If the pump is actuated during an anti-locking control, it first delivers a predetermined amount of pressure fluid to the reservoir. Because the brake conduit (through the master cylinder under a pedal force) is under a high pressure, the pressure fluid admitted to the reservoir, during a braking operation, cannot return to the brake conduit. This will involve the advantage that no damage can be done to the sealing sleeves of the master cylinder pistons. The pressure fluid introduced into the reservoir will only get back into the brake circuit once the driver has terminated the braking operation, withdrawing the pedal force acting upon the pedal.
Another object of the invention, therefore, resides in integrating a reservoir of this type into the pump casing.
The afore-mentioned object is realized by the present invention. Further advantageous embodiments are concerned with the check valve, a filter, the configuration of another annular chamber to insure a better connection of the outlet of the pump to the brake conduit system, and with a screw-in aperture enabling the pump set to be adapted to the vehicle braking system.
According to another embodiment, a switch valve is integrated in a valve carrier to block a by-pass conduit leading to a restrictor in the brake conduit. As soon as the pump starts to deliver, the restrictor causes a pressure drop so that the differential pressure on the inlet valve is reduced. This measure, equally, causes a noise reduction.
The invention will now be described with reference to the following figures.